The present invention relates to tube sockets and more particularly to tube sockets adapted to be used with tubes having balanced filament feeding and which are so constructed as to be able to accommodate high power requirements (including filament currents on the order of 250 amperes), high frequencies (up to 150 megacycles), and withstand high shock or gravatational requirements (on the order of 18 G's).
In electron tube applications, such as amplifiers, oscillators and the like, involving very high frequencies, designers of prior art tube socket assemblies, such as that disclosed in U.S. Pat. No. 2,427,563 to Lavoie, have recognized the advantages of utilizing an integrated structure by "sandwiching" bypass capacitors and connectors. Such a construction affords paths of low impedance for tube element connections to ground without necessitating externally placed capacitors and the resultant wiring problems. In addition, the patent to Lavoie stresses the need for keeping the length and inductance of the leads to the tube elements and between stages to a minimum to avoid objectionable regeneration and parasitic oscillations by stray electrostatic or magnetic coupling and by the effect of a common impedance between stages when a single power supply is used. This is accomplished in Lavoie by providing an integrated tube socket comprising a plurality of metallic stacking plates arranged in spatial relation to contact corresponding terminals on a tube, separated by suitable dielectric elements so as to constitute bypass capacitors which may be connected to ground and to the appropriate external circuit components to provide the aforementioned low impedance paths to ground.
Another example of a known tube socket assembly having integrated bypass capacitors positioned between the tube contactors is shown in FIG. 1. The socket assembly 100 shown in FIG. 1 comprises a base plate 102, a screen contact ring 104, a grid contact ring 106, and a ground ring 108. Positioned between the base plate 102 and contact rings 104, 106, 108 are bypass capacitors 110, 112, and 114. Located beneath the tube, which is shown by phantom lines, is a filament contact 116 supported by a plastic filament support 118 which in turn is supported by a cathode contact ring 120. The cathode contact ring 120 has a cylindrical extension 122 which provides electrical contact with the tube. Electrically connected to the anode of the tube is the anode contact ring 124. A plurality of threaded rod and nut constructions secure the assembly together to provide an integrated tube socket assembly.
Another concern of tube socket designers is that in operation of tubes at high frequencies using direct heating (i.e. introducing the signal at the filament) it is desirable to feed the modulated signal across the filament using a "balancing" technique. Balancing introduces the signal into each of the two leads of the filament in synchronous fashion. To introduce the signal across the two leads, capacitors are utilized. Although integration of the components into the assembly is desirable, it is impracticable to utilize wafer thin, "sandwiched" bypass capacitors, such as shown in FIG. 1, due to the nature of the assembly; i.e. the capacitors are not connected to a ground plate or connector. Accordingly, balancing has been achieved using external capacitors to feed the signal into the tube socket for entry at the filament. However, the wiring or leads connecting the externally located capacitors have caused problems due to the introduction of stray inductance and capacitance. At high frequencies the size of the leads and lead length is critical in avoiding resonance problems developed by the inductive and capacitive components associated with stray capacity attributable to the closeness of leads to ground and to each other.
Accordingly, it is an object of this invention to provide an integrated tube socket structure which minimizes lead lengths associated with balancing capacitors used in a filament feed for a high power, high frequency tube.
Another important consideration in the design of a tube socket is the provision of passages for allowing cooling air through the interior of the socket assembly to the tube. U.S. Pat. No. 2,977,494 to Johnstone, et al., discloses the use of annular slots or ducts formed in a base plate to provide for the passage of cooling air within the tube socket directed so as to strike the tube. Similarly in tube sockets of the prior art, elaborate measures have been utilized to provide a cooling effect. U.S. Pat. No. 3,042,893 to Chin, et al., discloses channels formed in the vicinity of the tube base. However, one potential disadvantage when utilizing tube socket constructions having the above mentioned provisions for cooling the tube is that the RF developed during high frequency usage may be transmitted through such cooling openings into the socket assembly so as to interfere with the functioning of the terminals exposed by the openings.
Accordingly, it is an object of the present invention to provide a tube socket assembly which incorporates annular cooling holes for cooling the anode which are so configured as to prevent RF from entering the tube socket assembly.
Another object of the present invention is to provide a tube socket assembly which incorporates an assembly of low inductance annular plates wherein the capacitance required by the various connectors is physically integrated into the tube socket structure.
A further object of the present invention is to provide a tube socket having a balanced filament feed provided by integrally contained capacitors so as to minimize stray inductance and capacitance when the tube is operating at its operating frequencies. Furthermore, because the length of the path of travel of currents through the tube socket assembly is significant at high frequencies, another object is to equalize the paths of travel of the signal as it is introduced into each of the two leads of the tube filament.
Still another object of the present invention is to provide a tube socket having contact rings which are fabricated with sufficient strength to support the tube when subjected to shocks exceeding 18 G's and having sufficient mass to transfer tube element heating from the metal/ceramic seals of the tube, and to maintain the seal temperature below manufacturer's specified temperature (approximately 250.degree. C.) when operated under worst case conditions.
Additional objects and advantages of the invention will become apparent to those skilled in the art upon further review of the following description of the invention.